1. Field of the Invention
This invention relates to novel compounds useful as redox indicators in chemical and biological systems and as dyes in photographic, photothermographic, thermographic, and pressure-sensitive processes. Additionally, it relates to the use of said novel compounds in producing photographic, photothermographic, thermographic, and pressure-induced images.
2. Background Art
Photographic systems employing liquid development to produce the final image as well as photothermographic and thermographic systems utilizing dry processing, that is, processing without the use of liquids, to generate the final image are well known in the art.
For each system, a number of different processes for producing color images have been proposed. See for example, C. C. Van de Sande, Angew. Chem. Int., Ed. Eng. 22 (1983), pp.191-209 for a discussion of color imaging processes as applied in photographic systems, Neblette, Imaging Processes and Materials, 8th Ed., Van Nostrand Reinhold, N.Y., 1989, Ch. 9, p.290 for an overview of processes for producing color images applicable in photothermographic systems, and U.S. Pat. No. 4,536,219 which discusses various known processes for forming color images in thermographic applications.
Among the processes of commercial significance for producing color images in photographic systems is the dye developer system. As is now well known and discussed in U.S. Pat. No. 2,983,606, the dye developer system relies upon the use of a molecule comprising a developer moiety such as a hydroquinone or p-aminophenol moiety which is linked usually by an insulating group to a dye or color-shifted dye moiety. The main function of the insulating group is to electronically insulate the dye portion of the molecule such that redox changes within the developer moiety do not affect the chromophoric or colored state of the dye moiety directly. Generally, there is little or no change in color between the oxidized and reduced forms of the dye developers.
In photographic systems for forming color images employing dye developers, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Development of the exposed silver halide results in oxidation of the dye developer to provide an oxidation product which is appreciably less diffusible than the unreacted dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image.
Another method for forming a color image, disclosed for use in photographic systems, is described in Japanese Pat. Application Laid-Open No. 58/97,044 [83/97,044] of S. Ikeuchi et al which has a Laid-Open date of Jun. 9, 1983. In the method described therein, a photosensitive element is employed which comprises a silver halide emulsion layer and a colored dye such as a substituted triarylmethane sulfonamide which in combination with the emulsion forms a color image. Image formation is effected by imagewise exposing the photosensitive element, developing with a developer in alkaline solution thereby forming an oxidation product of the developer in an imagewise distribution corresponding to the imagewise exposure of the emulsion and reacting the oxidation product of the developer with the colored dye to oxidize the colored dye. The oxidized dye then loses its color irreversibly by hydrolytic reaction with the alkali in the developing solution. The color image is formed by that portion of the colored dye that remains unoxidized and thus is not susceptible to base hydrolysis. It should be noted that if this system starts with the dyes in the photosensitive layers, the light absorption by the dye will reduce the light sensitivity of the system.
Among the processes for producing color images in thermographic and photothermographic systems are those of the metal salt type which employ moderate heating to develop a visible image and which comprise an oxidation-reduction image-forming combination comprising, e.g., an oxidizing agent such as the silver salt of a long chain fatty acid and a color-developing agent as the reducing agent for the silver ions, e.g. indoaniline or phenolic leuco dyes. These and other means for generating dye images in metal salt materials have been described by J. W. Carpenter and P. W. Lauf in their review of "Photothermographic Silver Halide Systems", Research Disclosure, No. 17029, June 1978.